1. Field of the Invention
The present invention relates to a molding body and the fabricating method thereof in which resin is supplied to the annular molding portion of a primary molding body thereby to form a secondary molding body integrally with the primary molding body.
2. Discussion of Related Art
In the case of fabricating a molding body by forming a packing as a secondary molding body integrally with a primary molding body, the molding body is formed in a manner that an annular molding portion is formed on the primary molding body and then fused elastomer is injected in the annular molding portion by using the primary molding body as a drag or female mold.
FIGS. 8 to 11 are diagrams showing the conventional method of fabricating such a molding body. An annular molding portion 2, shown in FIGS. 10 and 11, is formed on the bottom surface of a primary molding body 1. The annular molding portion 2 is formed in such a manner that erected wall portions 3 are provided in an opposed state on the bottom surface of the primary molding body 1 to form the annular molding portion 2 between the erected wall portions 3. The annular molding portion 2 is provided with a gate opening (not shown) for injecting the fused elastomer (fused resin) within the annular molding portion 2 and is also provided with an overflow opening 4 for allowing the fused resin to flow out of the annular molding portion. The overflow opening 4 is located on the opposite side of the gate opening so that the tip end portion of the fused resin injected into the annular molding portion from the gate opening flows out through the overflow opening so that the fused resin is filled entirely within the annular molding portion 2.
In the case of forming such a molding body 8, the bottom surface of the primary molding body 1 is brought into contact with a die or metal mold and the fused resin is injected through the gate opening into the annular molding portion 2. The injected fused resin 6 is divided into two flow paths within the annular molding portion 2, one flowing in the left direction from the gate and the other flowing in the right direction from the gate. Then, as shown by arrows 6 in FIG. 10, the two paths of resin join at the overflow opening 4 from the left and right direction. Thereafter, the tip portion of the fused resin flows out from the overflow opening 4. Once the resin has flowed out through the opening 4, it is determined that the annular molding portion 2 has been filled entirely with the fused resin. Thereafter, the fused resin is cooled so that the elastomer with elasticity is formed.
In FIG. 11, a reference numeral 7 depicts an elastomer serving as a secondary molding body formed in the annular molding portion 2. When the elastomer 7 is integrally formed with the annular molding portion 2 in this manner, the fabrication of the molding body 8 is completed. After the fabrication of the mold body as described above, the resin that overflowed through the opening 4 is cut and removed.
FIG. 9 is a diagram showing the state where the molding body 8 fabricated in this manner is attached to a unit or device 5. When the molding body 8 and the unit 5 are pressed to each other, the elastomer 7 closely contacts the unit 5, so that the elastomer 7 serves as a packing for establishing a seal between the molding body 8 and the unit 5.
According to such a molding method, in order to ensure a proper seal, the overflow opening 4 cannot be formed so that it is flush with the bottom surface of the primary molding body 1. Thus, a gas pocket is likely generated at the time of molding the fused resin, so that the fused resin cannot flow smoothly within the annular molding portion 2 due to the presence of the gas pocket. Further, when the length of the two flow paths from the injection gate to the overflow opening 4 differ from each other, the two flowpaths will merge together at a location that is displaced from the overflow opening 4. As a result, the resin 6 flowing through the two paths cannot flow smoothly through the overflow opening 4. If such a phenomenon occurs, shrinkage of the resin 7 results and welds are generated, so that the intensity of the drawing tension of the secondary molding body is degraded. As a result, the secondary molding body is likely to be cut. Further, as shown by a circle 9 in FIG. 11, there arises a problem that the close adherence between the erected wall portions 3 and the elastomer 7 can not be achieved.
Accordingly, an object of the present invention is to provide a molding body and a fabricating method thereof in which the secondary molding body, which is integrally formed with a primary molding body, does not experience shrinkage or the generation of welds. Another object is to ensure that the leading end of the resin flows through an overflow opening so that the secondary molding body is completely formed.
In order to achieve the aforesaid objects, the molding body of the present invention is characterized in that resin is molded within an annular molding portion provided on a primary molding body to form a secondary molding body integrally with the primary molding body. According to the invention, the annular molding portion is provided with a gate opening and an overflow opening and defining two flow paths therebetween. One of the paths is set to have a larger flowing distance and/or resistance than the other flow path, and the overflow opening is arranged in a manner that a length of the overflow opening facing the flow path having the larger flowing distance and/or flowing resistance is made larger than a length thereof facing on the other flow path.
In the present invention, since the overflow opening is arranged in this manner, the resin of the two flow paths can surely join at the overflow opening and then flow out of the overflow opening even when the flowing distances and/or flowing resistances of the two flow paths of the resin differ from each other. Thus, shrinkage of the resin and generation of welds in the resin are avoided. Thus, the intensity of the drawing tension is not reduced. Further, since a gas pocket is prevented from being generated, it is not necessary to lower the overflow opening to the bottom surface of the primary molding portion in order to prevent the generation of the gas pocket, so the resin can surely perform the sealing property.
According to the invention, the secondary molding body is made of elastomer. Therefore, when the elastomer has been molded, the resulting secondary molding body is elastic, so that the secondary molding body can function as a seal with the unit or the like.
The method of fabricating a molding body is further characterized in that the molding body is formed in a manner that flowing distances and/or flowing resistances of two flow paths of the resin from the gate opening to the overflow opening are adjusted to be substantially the same. Therefore, the resin of the two flow paths can surely join at the overflow opening and then flow out through the overflow opening. Therefore, the molding can be performed without generating shrinkage and welds in the resin.